Measuring rotary motions and, in particular, the speed and the rotational behavior of the individual vehicle wheels is of great importance in connection with automotive vehicle control systems such as systems for anti-lock control brake systems (hereinafter ABS), traction slip control, and suspension control, etc. Sensors for these types of applications must be durable, reliable, inexpensive to manufacture, easy to assemble, easy to diagnose, replace, and maintain.
There already exists a multitude of sensor types and sensor designs. Commercially available vehicles with electronically controlled anti-lock and traction slip control systems are primarily with inductive wheel sensors. These sensors are arranged on the periphery of a toothed disk rotating with the wheel. Inductive sensors generate a magnetic field.
As the toothed disk moves past the sensor, the magnetic field is modulated and a voltage is induced inside a coil within the sensor. The frequency and amplitude of the voltage allows measurements of rotary motion. As a rule, however, only the frequency or change in frequency is evaluated for determining the wheel speed.
Sensors of this type are relatively expensive and intricate. They require precise adjustment as a certain air gap must be maintained. The electric connection, the mechanical strength of the wires and the screening, the soiling and damaging of the toothed disks, corrosion, penetration of humidity etc. provide problems. Maintaining the necessary space requirements between the sensor and the toothed disk likewise often creates problems.
There are also known so-called wheel bearing sensors where the sensor and the pulse generator ring or the toothed disk are integrated into the wheel bearing. Thus the space constraints on the bearing style sensor size are highly demanding. Moreover, advantages are associated with bearing style sensors with regard to the expenditure of manufacture and assembly. A disadvantage is the poor accessibility of the built-in sensor which complicates sensor repair or replacement.
It is an object of this invention to overcome the disadvantages of known bearing style speed sensors for measuring rotary motions and to develop a measuring device characterized above all by a simple structure as well as by a comparatively small expenditure in terms of manufacture and assembly. Dismantling or replacing the sensor for purposes of checking or repair is made relatively easy.
This object is obtained by designing a sensor in the form of a plug or plug-like component and the sensor holder is designed in the form of a stationary sensor-accommodating housing which accommodates the sensor, positions the sensor at the signal generator ring, and keeps it in this position.
In accordance with a preferred embodiment of the present invention, the sensor is held in the sensor-accommodating housing by a snug fit, press fit, click-in mechanism, by a plug connection or by a similar measure. This allows the sensor to be assembled and dismantled with minimal effort.
Preferably, the sensor-accommodating housing has a recess at the point where the sensor will interact with the signal generator ring so that, for instance, a small air gap can be adjusted between the sensor or the pole shoe of a sensor and the passing teeth of a toothed disk (which serves as signal generator ring). With a closed housing the material thereof is selected so that the passage of the field lines whose change is evaluated for measuring the rotary motion will be minimally obstructed.
The present inventive measuring device allows a particularly advantageous design in the form of an active or passive wheel bearing sensor. In this case, the signal generator ring consists of evenly distributed teeth or corresponding recesses, arranged at or on a wheel bearing ring (e.g. on an outer ring of a wheel bearing which rotates with the wheel). The sensor holder is preferably mounted on the stationary wheel axle by means of a lateral flange, a corresponding ring, a disk or the like.
In a further embodiment of the present wheel bearing sensor, a stationary protective housing is provided which partially or completely surrounds the signal generator ring and which houses the sensor-accommodating housing and which, by way of a lateral flange or the like, is connected with the stationary wheel axle or a stationary part of the wheel support or wheel bearing such as the inner ring of the bearing.
In the present invention the plug-like structure of the sensor will prove particularly favorable because the sensor is easily mounted and dismantled on the wheel bearing despite the typical space constraints.
In another embodiment of the present invention, the sensor is shaped in the form of an oblong body (such as that of a pin) with a round, an angular rounded cross-section or in the form of a corresponding pin with a stepped cross-section. These structures promote the insertion and dismantling of the sensor in the sensor-accommodating housing.
According to this invention, the sensor can be positioned either parallel to the axis of rotation or wheel bearing axis or at an acute angle with regard to the same. This enables an optimal adaptation to the available space.
Another essential advantage of a wheel bearing sensor constructed in accordance with this invention consists in that the sensor will, at most, have a minimal influence on the construction of the bearing. This enables the same bearing design to be used both with and without a speed sensor which, for instance, will have a favorable influence on the manufacturing cost of the vehicle because only one bearing design needs to be stocked.
The plug-type design of the sensor of the present invention enables a permanent connection between the connecting cable and the sensor. No coupling is needed which, at the wheel, would require a special high reliability and, hence, an expensive construction because of the vibrations ensuing at the wheel. If a plug coupling is convenient, it will be possible to relocate the same to a safe spot remote from the wheel bearing sensor.